Pesticides are used for controlling insects, weeds, fungi, and/or other pests which destroy agricultural crops. Pesticides are widely used in fruits and vegetables because of their susceptibility to insect and disease attacks. Widespread use of pesticides in commercial agriculture has led to an increase in farm productivity.
The rapid development of agriculture in Saudi Arabia has resulted in a marked increase in the use of pesticides in agriculture. Among commercial pesticides, organophosphorus (OPs) and synthetic pyrethroid are widely applied on vegetables and fruits to control pests infestation.
Since pesticides are potentially harmful to the environment and consequently to human beings through the consumption of pesticide contaminated food, governments and international organizations established maximum residue limits (MRLs), based on the assumption that good agricultural practices are applied in the use of pesticides in farming, for pesticide residues in foodstuff (standard authority such as Codex Alimentarius Commission™ 2009 and World Health Organization™). When these chemical compounds are applied according to good agricultural practices, MRLs are not exceeded, but their incorrect application may leave harmful residues, which involve possible health risk and environmental pollution. Therefore, residues of pesticides in food products can affect the ultimate consumers especially when these products are freshly consumed.
TABLE AMaximum Residue Limits (MRLs) in mg kg−1 (ppm) fortargeted pesticide residues in/on selected food products.Maximum residue limits (MRLs)Targeted pesticidePotatoesOnionsGrapesDatesMalathion0.5888Pirimiphos-methyl0.05110.1Cypermethrin0.050.12Zero(Source: Codex Alimentarius Commission ™)
The total dietary intake of pesticide residues which remain on agricultural commodities are known as carcinogens (Cabello G et al. 2001 and Mills P et al. 2005) and are very harmful toxins because of their potential long-term adverse affects (Bolognesi C, Morasso G 2000).
Residual pesticides on fresh vegetables and fruits decrease by various culinary applications or with time, depending on the type and properties of the pesticides. Several investigators have found that levels of some pesticide residues were reduced by the pre-harvest intervals and/or culinary application, such as washing, peeling, cooking, boiling and storage (Cengiz M et al. 2007).
Moreover, these techniques in some cases are unsuitable for removal of residual pesticides adhering to surfaces of vegetables and fruits and/or present in plant tissues (Sances F et al. 1992).
Ionizing radiation (gamma-ray, x-ray and electron beam) is an important technology in food industry for preservation of a variety of fruits and vegetables (CAST, 1996). Low doses of ionizing radiation up to 1 kGy can inhibit sprouting in potatoes (Auda H, Khalaf Z 1979), onions (Elias P, Cohen A 1983); control the insects in dry fruits like dates (Azelmat K et al. 2006) and improve the storability of grapes (Al-Bachir M 1999). Irradiation doses below 2 kGy have been used to prolong shelf-life of fruits (Al-Bachir M 1999).
Medium doses (2-7 kGy) can improve technological properties of grapes (increase juice yield) and enhance anthocyanin extraction from grapes (Ayed N et al. 2000).
However, depending on the level of security required in commercial operations, fruits can receive up to three times the minimum absorbed dose for disinfestations (Hallman G 2001). On this basis, irradiation to 4-6 kGy can be used for decontamination (and disinfestation) in commercial processing of dates and can replace the currently established practice of fumigation with highly toxic chemicals (Grecz N et al. 1988).
TABLE BAbsorbed doses accepted in USA by the Food andDrug Administration ™ (FDA).ProductApproved useDose (kGy)White potatoesSprout inhibition0.05-0.15FruitsDisinfestations; ripening1 (maximum)delay.Improving technology2-7properties (Grapes)Vegetables, freshDisinfestations1 (maximum)
Ionizing radiation from electron beam accelerators or gamma ray sources is an efficient process for oxidation removal of organic pollutants. Compared to other Advanced Oxidation Process (AOPs), this technique has the advantage that no chemicals have to be added to the treated product. In addition, an alternative technique for the treatment of the wastewater is electron beam irradiation in combination with other conventional treatment methods. In the electron beam process, the organic materials react with the radicals generated by water radiolysis and the degradation products can be easily removed by conventional biological or chemical treatment (Pikaev A et al. 1997).
Irradiation of water by high-energy electrons or gamma rays results in the formation of two reducing species, the aqueous electron e−aq, and the hydrogen atom, H., and one oxidizing species, the hydroxyl radical, .OH, according to Equation 1 (Spinks J, woods R 1990).H2O-\/\/→[2.6]e−aq+[0.6]H.+[2.7].OH+[0.45]H2+[0.7]H2O2+[2.7]H30+  (1)
The number in brackets in Equation 1 is referred to as G values and are the number of radicals, molecules, or ions that are formed (or destroyed) in a solution absorbing 100 eV (energy). The effectiveness of this process in destroying organic compounds results from the rapid reaction of one or more of these species with the solute of interest.
The chemistry that is of principal importance with respect to the gamma radiolysis or electron beam processes in aqueous solutions and/or in food products is related to these three reactive species (i.e. e−aq, H. and .OH).
The major reaction in the water radiolysis involve the formation of e−aq, .OH and H. and in the presence of oxygen also O2.-, reactive intermediate, for example the reaction of e−aq and H. with O2 is rapid and results in the formation of the super oxide ion-hydroxyl radicals according to Equations 2 and 3 (Cooper J et al. 1993).e−aq+O2→O2.-  (2)H.+O2→HO2.  (3)
The effects of ionizing radiation on pesticides in aqueous solutions or in organic solvents are reviewed by many researchers (Abdel Aal E et al. 2001, Basfar A et al. 2007, Basfar A et al. 2009, Drzewicz P et al. 2004, Drzewicz P et al. 2004, Mohamed K et al. 2009 and Varghese R et al. 2006), but limited investigations of this nature have been performed for irradiated food (Bachman S, Gieszczynska J 1982, Carp A et al. 1972, Carp A et al. 1972, Cichy R et al. 1979, Cin D, Kroger M 1982, Lan R at al. 1976, Lepine F 1991 and Solar J et al. 1971).
Fruits and vegetables form an important component of human diet. Being rich sources of vitamins and minerals, fruits and vegetables add quality to human diet and increase its nutritive value. For these reasons they have also been termed as protective foods. The water activity in most fruits and vegetables is very high. Therefore, most fruits and vegetables are highly perishable. Fruits and vegetables play host to several micro-organisms and insect pests, supporting their growth and proliferation. Often fruits and vegetables harbor pathogens and parasites that may endanger human health. They may also harbor insect's pests of quarantine importance resulting in trade restrictions in export markets. They may be also contaminated with pesticides because of the environmental and processing conditions under which they are produced.
Therefore, before they can be safely incorporated into other food products, the pesticides load should be reduced. Because “thermal treatment” can cause significant loss of flavor and aroma, a “cold process”, such as irradiation, is ideal. Research over the past 40 years has shown that irradiation can be used to destroy insects and parasites in grains, dried beans, dried fruits and vegetables; to inhibit sprouting in crops such as potatoes and onions; to delay ripening of fresh fruits and vegetables; to increase juice yield, and for improvement of re-hydration. Moreover, food is irradiated to provide the same benefits as when it is processed by heat, refrigeration, freezing or treated with chemicals to destroy insects, fungi or bacteria that cause food to spoil or cause human disease and to make it possible to keep food longer and in better condition in warehouses and homes. Irradiation has been proposed as an alternative to chemicals and other conventional treatments. It is interesting to notice that the pre-harvest pesticides will still be used and their chemical interaction with irradiation is unknown. Therefore, there is a chance that irradiation may decontaminate pesticides residues in selected food products.